1. Field of the Invention
This invention relates to a method for the preparation of preforms and hollow articles in single-row and multi-row preform and blow molds, respectively, and to an apparatus therefor. More particularly, the present invention relates to a method and apparatus, wherein a gripper assembly removes molded preforms either during a preform mold opening stroke or from a preform reheat unit, transfers the preforms through different processing phases, adding internal and external components during the transformation into hollow articles, and returns to a waiting position outside the preform molding or preform reheat unit.
2. Brief Description of the Prior Art
Heretofore, in conventional prior art molding machines, preforms are injected and transferred by their neck splits which are mounted beneath a horizontal transfer plate in an intermittent rotary motion of multi-station machines as described in U.S. Pat. Nos. 4,946,367 and 5,062,787. Apparatus described therein is dedicated to producing hollow articles in single-row molds. To increase production, the molder must acquire double-row rotary blow molding machines as described in U.S. Pat. Nos. 4,457,689, 4,941,816, and 5,062,787. Unfortunately, such machines evidence certain drawbacks, namely, the difficulty of mold interchangeability due to different swing radii and stack heights. In order to obviate such limitations, costly neck splits and neck split holders are required for each station. The rotary plates and the machine beds are required to be laid out for the higher clamping forces in the injection station. As a result, the increased inertia of the heavy construction and large swing radii of the transfer plates slows down the dead time of mold open index and mold close, thereby increasing the overall cycle times. Efforts to reduce dry cycle times have been made, as for example, by replacing the rotary tables through closed circuit conveyor devices as described in U.S. Pat. No. 4,895,509. However, once again, costly support jaws, mounted on slide guides, are required for each station linked together to transfer the preforms and containers through the forming phases in a rectilinear motion in equal distances and equal time intervals. In the rotary-type and chain-link-type method, all phases of preform molding, conditioning, stretch blowing, and discharging are also interdependent due to a common transfer movement. The larger the number and size of transfer components, the more machine component weight needs to be transferred, so resulting in slower dry cycles, and thus longer overall cycles.
The industry has recognized these limitations and has also recognized that containers can be conditioned, stretch blown, and discharged in a fraction of the time that it takes to mold the preforms. This discovery has led to a method and apparatus for injection stretch blow molding as described in U.S. Pat. No. 5,468,443, wherein a larger number of injection molding stations produce preforms to be conveyed to a lesser number of stretch blow molding stations. The drawback of this method and apparatus is that it requires neck split moving means for supporting and conveying neck splits adapted to hold-neck portions of each preform used to mold the hollow articles through all preform molding, conditioning, blow molding, and ejection stations.
Refinements of the aforementioned patent, U.S. Pat. No. 5,468,443, are described in U.S. Pat. Nos. 4,793,960, 5,753,279, and 5,744,176, wherein molded preforms are first inverted to be released onto carrier members of a transfer conveying system. The preform carrier members are spread to correspond to the blow mold center distances. The inverted preforms are then indexed through a reheating section to ascertain that the first batch of molded preforms enters the blow mold station with the same temperature profile as the following batches of simultaneously molded preforms. Once the preforms are stretch blown into final hollow articles, they are inverted again to release them in an upright position. The limitation of this technique resides in the fact that the molten preforms need to be inverted and to be put onto a multitude of neck-size-dependent carrier members. Spreading mechanisms are needed to widen the carrier members to the corresponding blow molding center distances and reheat ovens are needed for maintaining equal temperature profiles in the preforms which enter the blow molds consecutively. The bottom up stretch blow molding method is prone to preform-sagging and results in thinner bottoms and heavier shoulders in the hollow articles. A second inverted device is then needed to release the finished hollow articles in an upright position. The number of injection cavities vs. blow cavities remains at a fixed ratio which limits the processing flexibility for lighter-wall vs. heavier-wall containers. A further stretch blow molding concept is described in U.S. Pat. Nos. 4,372,910 and 4,470,796 in which molded preforms are picked up by two-row multiple gripper transfer devices, then inserted one row at a time into neck-size dependent collars of the respective closed circuit transportation system to be subsequently indexed to the conditioning, stretch blow and ejection stations. The drawback of this system is that the preforms have to be transferred in two steps, a first one to pick up the preforms and a second one to put the same onto neck-size dependent collars. The secondary transfer system is a common closed loop belt drive which does not allow any timing flexibility between the simultaneous conditioning and stretch blow phases to obtain maximum processing flexibility. As described in European Patent No. EP 0,768,166, the conditioning system is required to be twice as long as the stretch blow system to ascertain uniform temperature profiles for the first and second row preforms being introduced. The reduction of the number of blow cavities relative to the preform mold cavities is offset by the need of the number of additional transfer devices and neck-size-dependent collars. U.S. Pat. No. 4,197,073 teaches a method, wherein alternate sets of parisons are released into laterally diverging tracks before arriving at the blow-molding unit. Despite the reduction in the number of blow mold cavities, in the end, the number of blowing means is equal to the number of preform mold means. U.S. Pat. No. 4,209,290 teaches a method wherein blow molding cells are interposed between open injection mold halves and injection cores with their preforms descend into the blow molding cells to form finished bottles. The drawback of this method is that the preform-molding cycle is interrupted during the time it takes to blow-mold the bottles.
U.S. Pat. Nos. 5,731,014, 4,718,845, and 4,706,924 disclose a solution for gaining maximum utilization of molding machines by simply switching mold cavities than complete molds in both stack molds and single-face mold versions clamped between a fixed and movable machine platen. This solution works well in conventional injection molding machines. However, in stretch blow molding machines, secondary components such as conditioning rods, blow cores, stretch rods, and bottom plugs, etc. need to be introduced at a predetermined center distance row. European Patent No. EP 0,768,165-A2 teaches a method wherein mutually coupled mold plates, connected to a power transmission means, actuate through motion transferring means a double pair of mold halves. U.S. Pat. No. 4,941,816 describes a double row clamp molding machine, wherein each blow mold row is closed by lateral moving means. Subsequently, pan cake cylinders rise between the two rows and expand to apply the necessary clamp pressure against oppositely located clamping means. Both methods are limited to a fixed number of two rows of blow molds at a fixed machine-dependent center row distance.
U.S. Pat. Nos. 5,683,729, 5,110,282, 4,824,359, and 4,403,907 refer to cam-driven rotary pick and place assemblies, which simultaneously carry preforms and hollow articles through the blow molding and release phases. The limitation of such carrying means is that their rotary motion is interdependent, requires space modifying devices and, therefore, does not allow any timing and stroke distance flexibility between the various processing phases. U.S. Pat. No. 5,653,934 teaches a method wherein the linearly moving, article-engaging elements constitute an integral part of the mold, which do not allow any molding operation during the movement in and out of the molding machine.
A method for adding external components such as labels, handles, or valves to the preforms or hollow articles is described in U.S. Pat. Nos. 4,479,770 and 4,721,451, wherein components, such as labels, are picked up from dispensing heads by the label carrier shuttle and are moved rectilinearly into an open mold wherein they are released onto the mold cavity walls and returned in the same manner to the dispensing head position. The drawback of this method is that the normal blow molding cycle of rotary machines is interrupted to allow the time to introduce the labels into the open mold cavities. Typically, finished containers have to be evacuated first and new preforms need to be delayed from entering the open mold cavities. U.S. Pat. No. 4,983,348 partially overcomes this limitation by opening the upper mold half earlier and inserting labels into the open mold half while holding the previously blown and labeled work pieces or hollow articles in the lower mold half for the duration of the label transfer phase without increasing the overall machine cycle time. The drawback of this method is that only one mold half can receive labels and the distance between the work piece and movable blow mold halves needs to be sufficient to allow the dispensing mechanism to operate in between.
To add secondary components to preforms or hollow articles, U.S. Pat. No. 5,678,771 teaches a method wherein an insert is attached on the surface above the threads of a neck finish to maintain stability during and after hot-fill processing. The drawback of this method is that the non-oriented, amorphous neck finish portion beneath the attached reinforced insert can shrink and deform during the hot-fill phase. U.S. Pat. No. 4,988,472 teaches a method that prevents the afore-mentioned drawback. However, the insert is placed into a neckring portion of an open mold first and then over-molded with molten material, an operation that lengthens the overall cycle.
U.S. Pat. No. 4,847,129 teaches a method of molding a multi-layer neck-finish structure whereby the center layer consists of a high temperature polymer.
U.S. Pat. Nos. 5,651,933 and 3,939,239 teach a method wherein thermoformed sleeves are put on injection cores and are overmolded to obtain a multi-layer preform. The inner overmolded layer needs to be stiff enough to withstand the following injection pressures when injecting the outer layer. Thus, this method requires more costly inner barrier material and is more difficult to bond with the overmolded material.
U.S. Pat. No. 5,516,274 describes a movable blow mold clamp assembly permitting improved access for servicing.